Comet 3I/ATLAS Accelerates Past Mars at 155,000 mph: Orbiter Tracks Its Rare Hyperbolic Escape

Astronomers have utilised the European Space Agency's (ESA) ExoMars Trace Gas Orbiter to track comet 3I/ATLAS, the third confirmed interstellar object to enter the solar system, as it traverses the Martian orbit at speeds reaching 155,000 mph (250,000 km/h). The operation demonstrates a novel triangulation technique that significantly refines trajectory predictions for fast-moving celestial bodies.

A One-Way Journey Through the Solar System

Identified on 1 July 2025, 3I/ATLAS is on a hyperbolic trajectory. Unlike periodic comets that orbit the Sun, this icy wanderer is transiting the Solar System once before returning into interstellar space. At its current velocity, the comet would cover the distance between Earth and the Moon in less than two hours.

For scientists, the velocity presents a navigational challenge. Instruments must be aimed ahead of the comet rather than at its previous coordinates, requiring precise calculations to maximise the scientific data gathered during this brief encounter.

Mars Orbiter Delivers Ten-Fold Accuracy

Before September, Earth-based telescopes provided the only tracking data. That changed in early October, when ESA's ExoMars Trace Gas Orbiter joined the effort. Between 1 and 7 October, the spacecraft observed the comet as it passed within 18 million miles (29 million km) of Mars.

By triangulating its observations with those from Earth, astronomers achieved a tenfold improvement in trajectory accuracy. This marked the first time astrometric measurements from a spacecraft orbiting another planet were officially submitted to the Minor Planet Center database, which consolidates global asteroid and comet observations.

Repurposing Instruments for Planetary Defence

The orbiter's CaSSIS camera, normally used to capture high-resolution images of the Martian surface, was redirected towards the skies to track the comet against a starry backdrop. This unconventional use of the instrument required collaboration across ESA teams, from flight dynamics to science operations, to minimise error margins and refine the comet's ephemeris.

Although 3I/ATLAS poses no threat to Earth, the exercise served as a rehearsal for planetary defence. By combining Earth-based and spacecraft data, scientists demonstrated how the flexible use of existing missions can sharpen readiness for potential hazards.

Preparing for Future Cosmic Visitors

ESA continues to expand its toolkit for monitoring celestial objects. The Jupiter Icy Moons Explorer (Juice) is observing 3I/ATLAS in its more active state after its closest approach to the Sun, with data expected in February 2026. Meanwhile, the upcoming Neomir mission will address the observational blind spot caused by the Sun's glare, providing early warnings of near-Earth objects approaching from that direction.

Looking further ahead, ESA's Comet Interceptor mission aims to study a pristine comet, ideally an interstellar one. Each new object, like 3I/ATLAS, underscores that the Solar System is not isolated, and that rapid, adaptive tracking is essential for both science and safety.

Lessons From a Galactic Wanderer

Comet 3I/ATLAS offers a rare insight into galactic dynamics, reminding us that interstellar visitors can arrive without warning. By leveraging spacecraft beyond Earth orbit, scientists are honing the skills needed to respond to future encounters—whether they are scientific opportunities or genuine threats.